Generally, users of the Internet wanting high speed, broadband service can use DSL in many parts of the world. In areas where digital cable capability exists, cable modems provide another option. But there are large areas of the world—even the developed world—where neither option will exist for the foreseeable future. These are areas of relatively sparse population density. In those areas, lengths of cable run from telephone central offices tend to be long, thus slowing DSL speed, and, in turn, discouraging DSL deployment. Likewise the sparse population density discourages the installation of digital cable because of high cost per subscriber. It is estimated that approximately 30% of the roughly 100 million households in the US live in such areas.
Satellite service would seem to be the natural way to serve this population and, indeed, there have been several such businesses begun. Typical ventures to date have used existing Ku band satellites. These satellites have large continental sized beams rather than multiple small beams. If one wants to provide high speed service the number of subscribers that can be served per unit MHz. using large beams becomes uneconomically small. The way to fix that problem is well known. By going to a multibeam satellite, where multiple small beams cover the continent sized area rather that one big beam, one gets an effective multiplication of bandwidth. A given band of frequencies can be reused multiple times on the different beams so that the bandwidth is effectively multiplied by the number of beams divided by the reuse factor. Further, such multibeam operation effectively carries no power penalty. Comparing two different satellites with the same power, the first with one large continental sized beam and the other with multiple smaller beams covering the same area as the large beam, both satellites produce the same EIRP.
But providing multiple small beams calls for a large increase in the satellite aperture size—all other things being equal. If one considers tens of beams (say 40-60 beams) the size becomes higher than most consider practical today in Ku band. Hence one is driven to the use of Ka band—the next frequency band up from Ku reserved for FSS operation.
However, Ka band introduces its own problem—namely much higher rain degradation. To be sure rain degradation is important in Ku band as well but in most situations adequate availability is provided by using several dB of margin. In Ka band, however, 10 and more dB of rain degradation is not that rare an occurrence, and simply providing margin to overcome rain degradation seems impractical. Providing power margins of tens of dB for a rain degradation situation that may occur for less than 10% of the time is impractical and uneconomic. It is desirable to be able to consistently provide a communication link over nearly all environmental conditions without resorting to brute force application of a power margin sufficient to overcome environmental degradation.